Release 14 will mark the start of 5G work in the 3rd Generation Partnership Project (3GPP). 5G will consist of Long Term Evolution (LTE) evolution together with a new radio-access technology, which is referred to as “NR” in the following.
FIG. 1 illustrates an example proposed frame structure for NR. More particularly, FIG. 1 illustrates two downlink (DL) subframes 5A and 5B (of the proposed frame structure and DL control channel structure). Each of subframes 5A and 5B include a number of orthogonal frequency division multiplexing (OFDM) symbols 10. Subframe 5A includes a first OFDM symbol 10A, a second OFDM symbol 10B, a third OFDM symbol 10C, and a fourth OFDM symbol 10D. Similarly, subframe 5B includes a first OFDM symbol 10E, a second OFDM symbol 10F, a third OFDM symbol 10G, and a fourth OFDM symbol 10H. Although FIG. 1 illustrates one example proposed frame structure for NR, other frame structures are possible. According to other potential frame structures for NR, each subframe 5A and 5B may include any suitable number of symbols. As one example, each subframe 5 may have 7 symbols. As another example, each subframe 5 may have 14 symbols.
Subframe 5A is divided into a control region 15A and a data region 20A. In the example of FIG. 1, control region 15A includes first OFDM symbol 10A, which contains control information. Data region 20A includes first, second and third OFDM symbols 10B, 10C, and 10D, respectively, which contain data. Similarly, subframe 5B is divided into a control region 15B and a data region 20B. In the example of FIG. 1, control region 15B includes first OFDM symbol 10E, which contains control information. Data region 20B includes second, third, and fourth OFDM symbols 10F, 10G, and 10H, respectively, which contain data.
In the proposed frame structure and DL control channel structure shown in FIG. 1, control region 15A of subframe 5A contains physical downlink control channel (PDCCH) 25A and 25B. Similarly, control region 15B of subframe 5B contains PDCCH 25C. Although the example of FIG. 1 illustrates two PDCCH in control region 15A of subframe 5A and a single PDCCH in control region 15B of subframe 5B, control regions 15A and 15B may include any suitable number of PDCCH. In some cases, control regions 15A and 15B may include zero, one, two or more PDCCH. Although the example of FIG. 1 illustrates control regions 15A and 15B as having a single OFDM symbol 10A and 10E, respectively, control regions consisting of more than one OFDM symbol are possible. Following OFDM symbols 10A and 10E with control information in control regions 15A and 15B, respectively, data regions 20A and 20B start. With respect to subframe 5A, data region 20A includes physical data channel (PDCH) 30A, which corresponds to PDCCH 25A, as indicated by the use of the same pattern in PDCH 30A as for PDCCH 25A in FIG. 1. PDCH 30A is scheduled by PDCCH 25A. Data region 20A also includes PDCH 30B, which corresponds to PDCCH 25B, as indicated by the use of the same pattern in PDCH 30B as for PDCCH 25B in FIG. 1. PDCCH 30B is scheduled by PDCCH 25B. In the example of FIG. 1, PDCH 30A is a subframe aggregate that extends from subframe 5A into subframe 5B across OFDM symbols 10B to 10H, while PDCH 30B is contained entirely within subframe 5A across OFDM symbols 10B-10D. It is for further study whether OFDM symbols 10A and 10E of control regions 15A and 15B that carry control information can also carry data.
PDCCH to one particular user is carried on a subset of OFDM subcarriers. The mapping of PDCCH can either be distributed or localized (for simplicity, PDCCH 25A and 25B in the example of FIG. 1 are localized). PDCCH can carry, among other things, DL scheduling information indicating DL resources in the same subframe (as in the case of PDCCH 25B) and also subsequent subframes in the case of subframe aggregation (as in the case of PDCCH 25A, in which corresponding PDCH 30A is scheduled as a subframe aggregate). In the example of FIG. 1, a third PDCCH 25C is shown in the first OFDM symbol 10E of control region 15B of subframe 5B. PDCCH 25C is shown without corresponding DL PDCH (e.g., an uplink (UL) grant). A user equipment (UE) detects PDCCH addressed to it and derives from the scheduling information PDCH related information. A UE is not aware of PDCCH transmissions to other UEs.
Downlink reference signals (mainly Demodulation Reference Signals (DMRS), but potentially also other types of reference signals) should be transmitted early in the subframe to enable the receiver to perform early channel estimation, and by that reduce decoding time. Since the UE is not aware of PDCCH transmissions to other UEs, it does not know which subcarriers in the first OFDM symbol (e.g., OFDM symbol 10A of subframe 5A or OFDM symbol 10E of subframe 5B) are modulated. It is not straightforward to map PDCH to the first OFDM symbol of a subframe since PDCH would have to be mapped around other users' PDCCH, of which the UE is not aware. The same applies for reference signals. In addition, reference signals would have to be mapped around other users' PDCCH, of which the UE is not aware. This would lead to non-equally spaced reference signals with potentially large “holes” in frequency domain. An existing approach maps PDCH and reference signals starting with the second OFDM symbol (e.g., second symbols 10B or 10F in the example of FIG. 1) or, in case of a longer control region, with the OFDM symbol after the control region. Not transmitting reference signals in the beginning of the subframe also delays the time when the receiver can do channel estimation, and thus delays decoding.